1. Field of the Invention
The present invention relates to an ignition system for a two-cycle engine.
2. Description of the Prior Art
Various ignition systems for a two-cycle engine have been developed which can prevent the so-called reverse operation of the two-cycle engine, that is, the reverse rotation of the crank shaft of the engine. The ignition system usually includes an electric signal generator for producing an electric signal containing amplitude variations each appearing at a certain crank angle, that is, an angular position of the crank shaft, and an ignition pulse generator for generating an ignition pulse in response to each of the amplitude variations of the electric signal. As is well known, the electric signal generator includes a transducer positioned in the proximity of a rotational body or member rotatable in synchronism with the crank shaft. The transducer produces the electric signal in accordance with the mechanical position of the rotational body. Since, however, the transducer per se cannot distinguish the direction of the rotation of the crank shaft or the rotational body, the ignition pulse generator should be adapted to avoid producing an ignition pulse at such an ignition timing as to allow the reverse operation of the engine.
In a prior art ignition system, a so-called pulser coil is incorporated in an electric generator, or a dynamo, as the transducer. The pulser coil is positioned in the proximity of the rotor of the electric generator and is responsive to the variation of the magnetic field generated by the rotational movement of the rotor so as to produce the electric signal containing amplitude variations representative of the variation of the magnetic field. Thus, the electric signal has an electric phase corresponding to the mechanical angular position of the crank shaft, that is, the crank angle. When, therefore, the ignition timing is selected to be a small crank angle, at which the electric signal has a small amplitude, the ignition pulse generator is subject to erroneous operation due to external noises. When, on the other hand, the ignition timing is selected to be a large crank angle at which the electric signal has a large amplitude, the ignition timing at the reverse rotation of the crank shaft is within a reverse operation allowing an angular region in which the engine is allowed to operate in the reverse direction. When it is desired to avoid the reverse operation of the engine, the ignition pulse generator must distinguish the direction of the rotion of the crank shaft by means of another sensor for detecting the rotational direction of the crank shaft, with the result that the overall construction of the ignition system becomes large and complicated and accordingly costly.